Start by building an actual tree, then flatten that tree:
$array = array (0 => array ( 'id' => '1', 'parent' => '0', ),
1 => array ( 'id' => '2', 'parent' => '1', ),
2 => array ( 'id' => '3', 'parent' => '0', ),
3 => array ( 'id' => '5', 'parent' => '0', ),
4 => array ( 'id' => '17', 'parent' => '3', ),
5 => array ( 'id' => '31', 'parent' => '2', ),
6 => array ( 'id' => '32', 'parent' => '2', ));
/* Building a tree. We also save a map of references to avoid
searching the tree for nodes */
//Helper to create nodes
$tree_node = function($id, $parent) {
return array('id' => $id, 'parent' => $parent, 'children' => array());
};
$tree = $tree_node(0, null); //root node
$map = array(0 => &$tree);
foreach($array as $cur) {
$id = (int) $cur['id'];
$parentId = (int) $cur['parent'];
$map[$id] =& $map[$parentId]['children'][];
$map[$id] = $tree_node($id, $parentId);
}
//Now recursively flatten the tree:
function flatter($node) {
//Create an array element of the node
$array_element = array('id' => (string) $node['id'],
'parent' => (string) $node['parent']);
//Add all children after me
$result = array($array_element);
foreach($node['children'] as $child) {
$result = array_merge($result, flatter($child));
}
return $result;
}
$array = flatter($tree);
array_shift($array); //Remove the root node, which was only added as a helper
print_r($array);
